RAISE project aims to investigate and assess Partial Discharge and breakdown behaviour of electric insulation in electrical machines windings. In the last years, the need for high power density and efficiency has become a central concern in all industrial sectors. For this reason, the arrival on the market of new power devices based on wide bandgap (SiC and GaN) semiconductors, with extremely short switching times, has raised a relevant interest.
Aerospace industry is one of the main areas which can take advantage from these devices. According to the MEA concept, replacing the aircraft’s hydraulic/mechanical actuators with electrical drives yields an improvement in efficiency and power density, which means a reduction in weight, fuel consumption and noise/pollutants emission. However, some reliability issues may arise in this type of electric drives when higher voltage gradient are adopted, and the power cables, connecting the inverter to the motor, exceed the so called “critical length”.
In this case, steep rising and falling voltage pulses make the cables act like transmission lines, with waves travelling along the cables forward and backward. In fact, due to cable-motor surge impedance mismatch, damped high frequency ringing at the motor terminals occurs leading to dangerous overvoltage (almost twice the bus voltage), which may seriously affect the motor’s windings dielectric insulation. In particular, if the voltage between the stator windings’ turns exceeds partial discharge (PD) inception voltage, PDs occur on the surface of dielectric insulation causing progressive erosion until complete breakdown. Critical length is proportional to the switching time, therefore the recent availability of SiC and GaN devices with very short switching time made troublesome to use even cables of few meters length.
RAISE project comprehends the analysis and the experimental assessment of state-of-the-art insulation materials and systems used in aircraft applications. Models will be proposed to assess the voltage gradients and the magnitudes observed for typical converter – cabling – machine systems, along with the voltage distribution within typical electrical machine windings, and its dependency on machine’s key parameters, such as the number of turns, the winding method used and the stator length.
RAISE aims to offers solutions to improve the reliability of the electrical machines and drives without compromising the overall performance and efficiency. The results will permit to drawing up design, qualification and verification guidelines supporting the development of machines operating with wide-bandgap switches in aerospace environmental conditions.
The project comprehends 4 work packages, reflecting different project stages. Each work package consists of two or more tasks and it is supervised by a Work Package Leader in charge of controlling the correctness of the work and respect of the timeline.
- WP2: Assessment of Partial Discharge and Breakdown Behaviour of Components Exposed to High Voltage Gradients